Method of providing a field free region above a substrate during sputter-depositing thereon



3,526,584 UBSTRATE E. J. SHAW FIELD FREE REGION ABOVE A S DURINGSPUTTER-DEPOSITING THEREON Sept. 1, 1910- METHOD OF PROVIDING A 2Sheets-Sheet 1 Filed Sept. 25, 1964 a v k INVENTOR ZJJaI H/ M ATTORNEY3,526,584 UBSTRATE E. J. SHAW Sept. 1, 1970 METHOD OF PROVIDING A FIELDFREE REGION ABOVE A S DURING SPUTTER-DEPOSITING THEREON Filed Sept. 25,1964 v 2 Sheets- Sheet z mama.

United States Patent 3,526,584 METHOD OF PROVIDING A FIELD FREE RE- GIONABOVE A SUBSTRATE DURING SPUT- TER-DEPOSITING THEREON Everett J. Shaw,Hopewell Township, Mercer County,

NJ., assignor to Western Electric Company, Incorporated, New York, N.Y.,a corporation of New York Filed Sept. 25, 1964, Ser. No. 399,141 Int.Cl. C23c 15/00 US. Cl. 204-192 9 Claims ABSTRACT OF THE DISCLOSURE Asputtering method includes using a chamber containing a sputtering gas,a cathode of a film-forming material, an anode, and a gride positionedover an article to be coated positioned on the anode or on an articlesupport. During application of a sputtering potential between the anodeand the cathode, a voltage is applied to the grid to create anequipotential or field free zone overlying the article. Such zoneextends away from the article by a distance greater (preferably, atleast three times greater) than the mean free path of negative gas ionswithin the chamber. Sputtering, both reactive and non-reactive, takesplace through this zone to coat the article with a film.

The use of the above method and apparatus precludes damage to thearticle andor to films previously deposited on the article.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to methods of and apparatus for coating articles, and moreparticularly to reactive and non-reactive sputtering methods andapparatus for depositing metal and dielectric layers on articles,Without deleteriously affecting the articles.

It is often desirable to provide a substantially pure metal coating onan article. More specifically, in producing a thin film electricalcomponent, one production step may include depositing a metal electrodeon a dielectric layer of the partially formed component which may alsoinclude another metal layer deposited on a nonconductive substrate andunderlying the dielectric layer.

Likewise, it is often desirable to provide a dielectric coating on anarticle. More particularly when the article is a sensitive thin filmelectrical component, which may comprise thin metal and thin dielectricfilms alternately deposited on a substrate, it is often not onlyexpedient, but also necessary to provide a final protective orencapsulative dielectric coating on the component. The dielectriccoating may be, for example, a non-conductive metal oxide. Theprotective dielectric coating both shields the component from adverseenvironment conditions and electrically insulates the component fromother electrical apparatus assembled with the thin film component.

Description of the prior art Controlled cathodic sputtering of aputterable metal onto an article in an inert atmosphere results in thedeposition on the article of a substantially pure thin film of themetal. Similarly, controlled cathodic sputtering of a putterable metalonto an article in a reactive atmosphere, which may include a mixture ofan inert gas and a reactive gas, results in the deposition on thearticle of a thin coating comprised of a compound produced by thereaction of the sputterable metal and either the reactive gas or anactive species of the gas. The compound may be a metal oxide.

The completed, coated article may comprise alternating metal anddielectric layers produced by alternating such reactive and non-reactivesputtering steps. An ex- 'ice ample of one of the more complex types ofcoated articles formed by sputtering is a thin film electric capacitorwhich includes a non-conductive glass substrate or base onto which theremay be alternately sputtered a dielectric base layer, a first metalelectrode, a capacitor dielectric layer, a second metal electrode orcounter electrode, and a final dielectric layer which encapsulates andprotects the previously deposited layers (see Berry Pat. 2,993,266). Oneor more of the sputtered layers may be omitted; for example, deletion ofthe second electrode and the capacitor dielectric sputtering stepsresults in a dielectric encapsulated layer which may be patterned toproduce a thin film resistor.

It has been established as a result of extensive testing of articleswhich have been coated by prior art reactive and non-reactive sputteringmethods and apparatus that the physical characteristics of the articlesand of any coating previously sputtered thereon varied and deterioratedsignificantly from those characteristics existing prior to sputtering.

More specifically, metal portions of articles, such as metallicelectrodes of thin film resistors and capacitors onto which dielectriclayers have been reactively sputtered, showed a marked increase in ohmicresistance, indicating that some of the metal had been oxidized duringthe re active sputtering step. In addition, dielectric articles, such asthe dielectric layers of thin-film capacitors broke down in use,indicating the presence of pinholes in the dielectric material which hadnot previously been present. Such deteriorations of the physical andelectrical characteristics of the thin film electrical components werefound to be unpredictable, dilficult to control, and rendered many ofthe thin film components unsuited for use in electrical circuits.

SUMMARY OF THE INVENTION Research conducted in an effort to determinethe cause of such variations and deteriorations indicates that theundesirable oxidation of metal articles and the undesirable pinholesformed in dielectric articles by a sputtering step may both be obviatedby sputtering through a potential zone adjacent to the surface of thearticles which surface is to be coated during the sputtering operation.In addition,

by providing the potential zone, it is found that the reactive andnon-reactive sputtering operations could be performed at highersputtering voltages and in a shorter time than was hitherto possible byprior art methods and apparatus without deleteriously affecting thearticles.

An object of this invention is to provide new and improved methods ofand apparatus for coating articles.

Another object of this invention is to provide reactive and non-reactivesputtering methods of and apparatus for coating articles with dielectricand metallic coatings without deleteriously affecting the articles.

Still another object of this invention resides in a method of coatingthin film electrical components with a metallic or dielectric layerwherein deterioration of the electrical characteristics of thecomponents is avoided.

Yet another object of this invention resides in apparatus for depositingmetal or dielectric films on thin film electrical components whereinpreviously deposited metal and dielectric layers of the component arenot damaged.

A further object of this invention resides in the provision of apparatusfor producing a potential of a predetermined magnitude and polaritywithin a zone adjacent to an article during a reactive sputteringoperation for coating the article with a dielectric layer.

A still further object of this invention is to provide apparatus forproducing a zone having an electrical field with a predeterminedgradient directly over a metallic or dielectric article during anon-reactive sputtering step for depositing a metal layer on thearticle.

With these and other objects in view, the present invention contemplatesthe provision of grid-like facilities above an article mounted forcoating by sputtering apparatus which includes a sputtering cathode andan anode. Concurrent with the application of a negative sputteringvoltage to the cathode, a voltage is impressed on the gridlikefacilities to establish a potential of a predetermined magnitude andpolarity within a zone extending between the grid-like faciliteis andthe article. The potential zone is defined by a space of Zero or lowpotential gradient of either polarity extending between the grid-likefacilities and an article mount. To preclude damage to the articleduring the sputtering operation, the grid-like facilities are spacedfrom the article by a distance greater than the mean-free paths of ionsin the sputtering atmosphere.

Further, with the foregoing objects in view, the present inventioncontemplates a method of coating articles by reactive or non-reactivecathodic sputtering and simultaneously therewith producing a potentialzone of a predetermined magnitude and polarity immediately above thearticles. The method includes sputtering electrically neutral atoms of apredetermined material through the potential zone onto the articlewhereat the atoms alone or in combination with a reactive gas form acoating on the article without deleteriously affecting the article.

BRIEF DESCRIPTION OF THE DRAWINGS A complete understanding of thisinvention may be had by referring to the following detailed descriptionand the accompanying drawings illustrating specific embodiments thereof,wherein:

FIG. 1 is a cross-sectional, elevational view of a first embodiment of asputtering apparatus, including a cathode and an anode and showinggrid-like facilities positioned above an article mounted on the anodefor performing the method of the present invention to coat the articleaccording to the principles of the present invention;

FIG. 2 is a cross-sectional, elevational view of a second embodiment ofa sputtering apparatus similar to that shown in FIG. 1 in which thearticle is mounted on a support other than the anode;

FIG. 3 is an enlarged plan view of the grid-like facilities used in thesputtering apparatus shown in FIGS. 1 and 2 for establishing a potentialzone above the article;

FIG. 4 is an enlarged perspective view of a thin film capacitor which ismounted for coating either on the anode shown in FIG. 1 or on thesupport shown in FIG. 2 prior to being coated; and

FIG. 5 is an enlarged perspective view of the thin film capacitor shownin FIG. 4 illustrating alternating metal and dielectric coatingsprovided on a substrate according to the principles of the presentinvention.

DETAILED DESCRIPTION Structure In FIG. 4 of the drawings there is showna thin film electrical capacitor 10, which may be produced according tothe principles of this invention. The capacitor is used throughout thisdescription as an example of an article to be coated only because it isone of the more complex articles which may be produced by the presentinvention. The thin film capacitor 10 comprises a substrate or base 11provided with a dielectric base layer 12, a first metal electrode 13,and a dielectric layer 14 overlying the electrode 13. A second metalelectrode 15 overlies a portion of the dielectric layer 14. Referring toFIG. 5, the capacitor 10 is shown having upper surfaces 1616 which areexposed during a sputtering operation for receiving a coating, such as adielectric layer 17 of a metal oxide. All of the layers 12-17 of thecapacitor 10 may be deposited on the preceding layer according to theprinciples of this invention.

Referring now to FIG. 1 a grid-like facility, such as a screen 21 ispositioned within sputtering apparatus above an article to be coated,such as the thin film capacitor 10 the capacitor 10 may be mounted inany desired manner to position a surface, such as one or more of theupper surfaces 16, in line with the preferred path of atoms 59 which aresputtered from a cathode sheet 26 of a cathode assembly 22 uponapplication of a negative voltage to the cathode sheet 26 from a powersource 43. A predetermined voltage is applied to the screen 21 toproduce a controlled potential zone 23 between the screen 21 and thethin film capacitor 10 both of which may be mounted on an anode 24, oralternatively on a support 25 (FIG. 2), or in any other desired positionduring the sputtering operation. To preclude damage to the layers 1217of the capacitor 10, the height X of the zone 23 between the screen 21and the surfaces to be coated 16 of the thin film capacitor 10 isgreater than the mean-free path of ions a, 60b, 63a and 63b of gaseswhich may be used in the sputtering apparatus 20 during the sputteringoperation.

The cathode assembly 22 is comprised of the sheet 26 of a sputterablematerial such as tantalum or silicon and a backing plate 31. A frontsurface 29 of the sheet 26 faces in the general direction of thecapacitor 10, while a back surface 30 faces a backing plate or guard 31,the proximity of which to the back surface 30 of the cathode sheet 26substantially prevents sputtering of metal atoms' from that surfaceaccording to Paschens law. When a negative sputtering voltage is appliedto the cathode sheet 26, atoms 59 of the film-forming cathode materialare randomly sputtered from the front surface thereof.

The anode 24 may serve as a mount for both the thin film capacitor 10and the screen 21 during the sputtering operation. The thin filmcapacitor 10 is supported in such a manner that a portion of one or moreof the upper surfaces 16 thereof are selectively exposed by a mask 32 toreceive the atoms 59 which are sputtered from the cathode sheet 26.During the sputtering operation the anode 24 is maintained at apotential, such as ground potential, which is positive with respect tothe negative sputtering voltage impressed on the cathode sheet 26. Themask 32 is made of a conductive material and may be electricallyconnected by a wire 27 to the anode 24 or support 25 on which thecapacitor 10 rests.

Apparatus 120, similar to that depicted in FIG. 1, is shown in FIG. 2wherein similar elements are indicated by like reference numerals. Inaddition to the cathode 22 and the anode 24, there is provided acapacitor support 25 on which the capacitor 10 and the screen 21 mayrest during sputtering. The support 25 may be positioned in anydesirable manner within the chamber to expose the surfaces 16 throughthe mask 32 to metal atoms 59 sputtered from the cathode 22. The support25 may be maintaned at ground potential during sputtering. In thisembodiment the support 25 serves as a capacitor rather than the anode24, and hereinafter, the descriptive word mount will refer to both theanode 24 shown in FIG. 1, and the support 25 shown in FIG. 2.

Referring now to FIGS. 1 and 2, the sputtering apparat us 20 includes aconductive metal base 33 and an upright enclosure 34 mounted on ahermetic seal or gasket 35 provided on the base 33. The enclosure 34defines a sputtering chamber for containing the sputtering gas or gasesand surrounds the cathode assembly 22, the anode 24, the article to becoated, such as the thin film capacitor 10, the screen 21 and thesupport 25 if one is used. The enclosure 34 may be a conventionalupright bell jar 36 or may be of any other desired size and shape, suchas a chamber (not shown) of a continuous vacuum sputtering line (such asthat discussed in the Western Electric Engineer, April 1963, pages9-17).

A first conductive mounting post 39 extends upwardly from anelectrically insulating, vacuum-tight support 40 through the conductivebase 33 and supports the cathode sheet 26 in any desired position, suchas the generally horizontal position shown in FIGS. 1 and 2. The backingplate or guard 31 is supported by an electrically conductive tube 41which extends upwardly from the base 33 and surrounds without touchingthe mounting post 39.

A first electrical terminal 42 is attached to the first mounting post 39for connecting the cathode 22 into a sputtering power circuit 43. Asecond metal mounting post 44 extends upwardly from the base 33 forsupporting the anode 24 in any of several desirable positions withrespect to the cathode 22. In FIGS. 1 and 2, the anode 24 is shown in agenerally horizontal position. If the support 25 (FIG. 2) is used as amount for the capacitor during sputtering, an additional third metalmounting post 45 extends upwardly from an insulating support 47 throughthe base 33 to mount the support 25. Second and third electricalterminals 46 and 49 are attached respectively to the second and thirdmounting posts 44 and 45 for grounding the anode 24 and applying anydesired potential to the support 25 during sputtering. The anode 24 andthe cathode 22 may be positioned with respect to each other in a varietyof ways known in the art to be conducive to efiicient cathodicsputtering, such as in vertical or horizontal alignment, or at rightangles to each other. Likewise the cathode 22 and the article to becoated may be relatively positioned in various known manners, the onlyrequirement being that the article be positioned to receive diffusedatoms 59 sputtered randomly from the cathode 22. In FIGS. 1 and 2 thecathode 22 is in substantial vertical alignment with both the anode 24and the capacitor 10 mounted for coating so that the surfaces of thecapacitor, such as the upper surfaces 16, are positioned to receive thediffused atoms 59. In addition, the cathode sheet 26 and the anode 24are spaced apart a predetermined distance Z, the magnitude of whichdepends on such factors as the sputtering voltage, the composition andpressure of the sputtering gas used within the enclosure 34, and thetype of the material comprising the cathode sheet 26.

Non-reactive sputtering takes place within an inert atmosphere which maycomprise a noble gas, such as argon. Reactive sputtering takes placewithin a reactive atmosphere which may comprise a reactive gas mixtureincluding selected portions of an inert gas and a reactive gas. Amongthe inert gases which are suitable for use are argon and xenon, whileexamples of the reactive gases which are suitable for use are oxygen andwater vapor. A gas supply 50 is provided to introduce the reactive gasor the non-reactive gas mixture into the enclosure 34 to condition theappartus for the sputtering operation. The gases are normally comprisedof a majority of electrically neutral gas molecules 61a and 611;, butduring the sputtering step are ionized to produce gas ions which includepositive ions 60a and 63a, negative ions 60b and 63b and neutral gasmolecules and atoms 62a and 62b. Evacuation apparatus 51 is provided toevacuate the enclosure 34 during an inert gas flushing operation, duringintroduction of the sputtering gas or gases, and throughout thesputtering operation. If an non-reactive, inert gas is used in theenclosure 34, the atoms 59 sputtered from the cathode 22 impinge uponand coat an article such as the thin film capacitor 10 forming asubstantially pure metal layer, such as the layers 13 and 15 of thecapacitor 10. If a reactive gas mixture, such as one containing oxygen,is used, the atoms 59 sputtered from the cathode 22 combine withreactive gas molecules 61b at the surface of the article to be coated,such as one or more of the upper surfaces 16 of the thin film capacitor10 to form an dielectric layer, such as a metal oxide 17 thereon.

Referring now to FIGS. 1, 2, and 3, the grid-like facilities or screen21 are shown including a metal frame 52 which encloses and supportswoven strands 53-53 of a conductive metal which define meshes 5454. Theindividual strands 53 may be comprised of any electrically conductivematerial, such as tantalum, but are preferably of the same material asthe cathode sheet 26. The size of the meshes 5454 is relativelyunimportant to proper operation of the present invention, but ispreferably quite small to limit field penetration or non-linearity ofthe potential gradient of the potential zone 23.

Legs are attached to and extend from the frame 52 to position the screen21 above the thin film capacitor 10. The legs 55 may be electricalyconductive or nonconductive, and are of a length sufiicient to space thescreen 21 a predetermined distance X above the thin film capacitor 10.The distance X is greater than the meanfree path of the negative gasions b and 63b of the sputtering gas, and is preferably a multiplegreater than three of the ionic mean-free path.

Proper positioning of the screen 21 over the thin film capacitor 10defines the potential zone 23 which is bounded above by the screen 21and below by the capacitor mount such as the anode 24 or the capacitorsupport 25. The thin film capacitor 10 lies within the potential zone 23when resting on the mount 24 or 25.

During the sputtreing operation and when the screen 21 is positionedover the thin film capacitor 10, a screen voltage substantially equal tothe potential of the mount 24 or 25 is applied to the screen 21. Thescreen voltage may be applied through the electrically conductive legs55 which electrically contact the mount 24 or 25. Alternatively, if thelegs 55 are non-conductive the screen voltage may be applied through anelectrical connection 56 between the frame 52 and the mount 24 or 25.

With the legs 55 made of a non-conductive material, it may also be foundsuitable to connect an independent screen voltage source (not shown)directly to the screen 21 for selectively adjusting the screen voltage,in which case no direct electrical connection need be provided betweenthe screen 21 and mount 24 or 25.

Referring again to FIGS. 1 and 2, the sputtering power circuit 43 isshown including the variable voltage sources 69 and a series switch 70.The negative side 71 of the voltage source 69 is connected by a line 72to the first terminal 42 to apply the negative sputtering voltage to thecathode 22 via the post 39. The positive side 73 of the source 69 isconnected by a line 74 to ground. The mount voltage which may be groundpotential is in turn applied to the screen 21 by the legs 55 or by theconnection 56. The potentials applied to both the screen 21 and themount 24 or 25 being substantially equal, the zone 23 is renderedessentially equipotential and completely overlies the thin filmcomponent 10 which rests on the mount 24 and 25. Moreover, if theindependent screen voltage source is used, it maybe adjusted to impressa voltage on the screen 21 which is slightly different from that of themount 21 or 25 to provide a potential zone 23 having a small gradient ofeither polarity.

Operation In the operation of the apparatus, a component to beencapsulated, the thin film capacitor 10, for example, is placed on themount 24 or 25. The mask 32 may be provided to expose only selectedportions of the upper surfaces 16 of the capacitor 10. The screen 21 ispositioned over the component 10 by means of the legs 55 which rest onthe mount 24 or 25. If the connection 56 or the independent screenvoltage source are to be used, appropriate electrical connections aremade. The enclosure 34 is positioned over and sealed to the base 33 bythe seal 35. The enclosure 34 is evacuated by the evacuation apparatus51 flushed with an inert gas, whereafter the sputtering gas mixture isintroduced into the enclosure 34 from the supply 50. The switch isclosed to apply a sputtering voltage, such as 2,500 volts between thecathode 22 and the anode 24 from the source 64. The mount voltage isapplied to the screen 21 through the legs 55 or the connection 56 toproduce the potential zone 23. The screen voltage may be of any desiredpolarity but should be of a magnitude so that the zone 23 isequipotential or nearl so.

During the sputtering operation, electrons 64 are freed from neutral gasmolecules which have been ionized, for example, by cosmic radiation.These electrons 64 are accelerated by the field and strike the molecules61a-61b of the gas, producing additional gas ions such as the positiveions 60a and 63a and the negative ions 60b and 63b, and additional freeelectrons 64. Under the influence of the negative cathode potential, thepositive gas ions 60a and 63a move toward and strike the cathode sheet26 of the film-forming material to sputter the atoms 59 of thespu-tterable material therefrom. The atoms 59 of the sputterablematerial are sputtered randomly and many of the atoms 59 pass throughthe meshes 54 of the screen 21 and through the potential zone 23. Theatoms 59 reach the selectively exposed upper surfaces 1616 of the thinfilm capacitor 10. If a non-reactive gas, such as argon, is used, themetal atoms reaching surfaces 16-46 form metal layers such as the layers13 and 15 of the capacitor 10 shown in FIG. 4. If the reactive gasmixture, such as one containing oxygen and argon, is used, the metalatoms combine with the reactive gas to form dielectric layers, such asthe layers 12 and 14 or the layer 17 which encapsulates the capacitor 10as shown in FIG. 4.

Components, such as the capacitor 10, onto which the metal or metaloxide layers 12-17 are sputtered while the capacitor 10 is maintainedwithin the zero or low gradient potential zone 23, display littledeterioration such as electrode oxidation or dielectric pinholes. Inaddition, a larger sputtering voltage may be used to deposit the layers12-17 in a shorter time than has been hitherto possible withoutdeleteriously aifecting the component 10.

EXAMPLES The following examples of thin film components encapsulatedwith a dielectric layer according to the principles of the presentinvention are given to illustrate, without limiting, the possibleapplications of the present invention.

Example I Two resistor slides, A and B each having sixteen thin tantalumfilm resistors deposited thereon, were coated with a protective layer 17of tantalum pentoxide (Ta O in a reactive atmosphere comprised of amixture of argon and oxygen. Slide A was coated without a screen such asthe screen 21 in place; whereas a tantalum screen 21 was positionedone-half inch above slide B during the coating thereof in accordancewith the principles of this invention. The distance between the screen21 and slide B was greater than the mean-free path of the negative gasions 606 and 636 at the pressure and voltage used in the sputteringoperation. Slides A and B were sputtered until the Ta O layer 17 thereonwas 300-400 angstroms (A.) thick. In both operations, thecathode-to-anode spacing Z was approximately two and one-half inches andthe cathode 26 was tantalum. A comparison of the sputtering variablesand the resistance deteriorations after sputtering is shown in Table I.

8 as indicated by the relatively small (23%) change of resistance ofslide B compared with the high (3.82%) change of ressitance of slide A.

Example II Twenty thin tantalum film capacitors 10 were encap sulatedwith a layer 17 of Ta O Without a screen such as the screen 21 in place.Initially, the sputtering variables were a sputtering voltage of 1,000volts, current of 50 ma., and 15 microns of O 185 microns of Ar, for atime of 105 minutes; and subsequently 1,450 volts, ma., 15 microns of Oand 185 microns of Ar for 150 minutes. All the capacitors 10 were foundto be short-circuited after encapsulation, indicating that the capacitordielectric had been damaged during sputtering. The sputtering times usedwere necessary to produce a protective Ta O layer of suflicientthickness to provide protection.

Twenty thin tantalum film capacitors 10 were encapsulated with a layer17 of Ta O with the tantalum screen 21 in place according to theprinciples of the invention. The sputtering variables were a sputteringvoltage of 2,550 volts, a current of 80 ma., and 10 microns of O partialpressure, and microns of Ar, for 80 minutes. All the capacitors 10 wereusable after encapsulation, and showed an average leakage resistance of52 megohms. The average change in capacitance was 1.54%. The sputteringtime of 80 minutes produced a protective layer of Ta O suificient toprovide protection.

Conclusion It is apparent that with the screen 21 used during a reactivesputtering operation, in accordance with the principles of the presentinvention, it is possible to encapsulate capacitors 10 with a layer 17of Ta O of sufficient thickness without rendering the capacitorsunusable. Moreover, use of the screen 21 permits a higher sputteringvoltage to be used with the result that the sputtering time decreases.

One possible theory explaining the operation of the screen 21 may bethat when the free electrons 64 are repulsed by the cathode 22 tofurther ionize the sputtering gas, both neutral gas molecules 62a and62b, positive ions 60a and 63a, and negative gas ions 60b and 63b areformed. The positive gas ions 60a and 63a, as discussed in the precedingparagraphs, are effective to sputter atoms 59 from the cathode 22. It isthough that the negative gas ions 60b and 63b are accelerated by thepotential gradient between cathode 22 and anode 24 toward the positivelybiased anode 24 and the article to be coated thereon. With no screen 21in place, the negative gas ions 60b and 63b attain a velocity suflicientto penetrate the layers 12-17 upon impingement with the capacitor 10.Thus, negative gas ions 63b of the reactive gas internally oxidize themetal layers 13 and 15 of the component, while negative gas ions 6% and63b of the TABLE I Before After Time Cur- O2 partial SputteringResistance Average Resistance Average Percent required Voltage rentpressure gas pressure range resistance range resistance of (minutes)(volts) (ma.) (microns) (microns) (ohms) (ohms) (ohms) (ohms) changeWithout grid in place Slide A.-- 1, 500 100 5 45 3, 309-3, 127 3, 209 3,455-3, 227 3, 331 3. 82 With grid in place Slide B 80 2, 550 75 5 18 3,461-2, 872 3, 009 3, 468-2, 876 3, 016 23 It is apparent that with thescreen 21 in place, a 300- 400 angstrom layer 17 of Ta O was produced ata higher voltage and therefore in a shorter time than when the screen 21was not used. Also less resultant variation or deterioration wasproduced with the screen 21 in place reactive and non-reactive gasespuncture the dielectric layers 12 and 14.

By providing the potential zone 23, spaced above the capacitor 10 by adistance X greater than the mean-free path of the negative gas ions 606and 636, there is, ac-

cording to Paschens law, great statistical probability that the neagtiveions 60b and 63b will undergo one or more collisions in the zone 23 withother particles. Should a collision occur, the negative ions 60b and 63blose much, if not most, of their kinetic energy through momentumtransfer. The zone 23, being of zero or low potential gradient preventsthe now low kinetic energy negative ions 60b and 63b fromre-accelerating. That is, the negative ions 60b and 63b after collisionare under the influence of an electric field having little or nogradient and undergo little or no accelerative forces. In addition, thefield free character of the zone 23 is thought to limit ionizationwithin the zone to a great extent, and provides a buffer zone in whichinitially accelerated negative ions 60b and 63b undergo a sufiicientnumber of collisions to reduce ionic velocity to nearly thermalvelocity. The supposed absence of any accelerative forces on the ions 6%and 63b after collision leads to the conclusion that should ions 60b and63b reach a surface of the article to be coated, their kinetic energywould be too low for the ions to penetrate the surface. Thus, theunwanted article deteriorations, specifically metal oxidation anddielectric puncturing, due to ion impact are prevented.

It is to be understood that the above-described arrangements are simplyillustrative of the application of the principles of this invention.Numerous other arrangements may be readily devised by those skilled inthe art which will embody the principles of the invention and fallwithin the spirit and scope thereof.

What is claimed is: 1. A method of coating an article with a layer of apredetermined material, the article being mounted on a support in ararefied, gas atmosphere which supports, be tween an anode and a cathod,a sputtering gas discharge, which method comprises:

sputtering through a zone particles of the predetermined material ontothe article to provide the layer on the article, said bone extendingaway from the article a distance at least as great as the mean-free pathof negative gas ions in the atmosphere; and

concurrently with said sputtering, positioning an electrode in thedischarge and impressing a potential thereon substantially the same asthe potential on the support to render said zone substantially fieldfreewhereby deterioration of the article and of the layer is prevented.

2. A method of coating an article with a layer of a predeterminedmaterial, said article being mounted on an anode in a rarefied, gasatmosphere supporting between the anode and a cathode a sputtering gasdischarge which includes negative ions, which method comprises:

positioning an electrode in the discharge and impressing a potentialthereon substantially the same as the potential on the anode toestablish a field-free region adjacent to the article and extending awayfrom the article a distance greater than the mean-free path of thenegative gas ions; and

sputtering electrically neutral atoms of the predetermined materialthrough said field-free region onto the article, said field-free regionprecluding re-acceleration of any negative gas ions which experiencecollisions therewithin.

3. A method of coating an article with a dielectric layer the articlebeing mounted on a support in a rarefied, reactive gas atmosphere whichsupports, between an anode and a cathode, a supttering gas discharge,which method comprises:

sputtering through a zone particles of a predetermined material towardthe article, said zone extending away from the article a distance atleast as great as the mean-free path of negative gas ions in theatmosphere;

reactively combining said particles and the reactive 'gas to provide thedielectric layer on the article; and concurrently with said sputtering,positioning an elec- 10 trode in the discharge and impressing apotential thereon substantially the same as the potential on the supportto render said zone substantially field-free whereby damage to thearticle and the layer is prevented.

4. A coating method for providing a thin film of a predetermined,sputterable material on a thin film component, the component includingthin dielectric and thin metal films deposited alternately on anon-conductive substrate, the component being mounted on a support in ararefied, gas atmosphere supporting between an anode and a cathode asputtering gas discharge which includes negative gas ions, which methodcomprises:

positioning an electrode in the discharge and impressing a potentialthereon substantially the same as the potential on the support toestablish a substantially field-free region adjacent to the componentand extending away from the component a distance greater than themean-free path of the negative gas ions, the field-free region having apotential gradient which is substantially zero; and

sputtering particles of the predetermined, material through saidfiield-free region onto the component, said field-free region beingeffective during said sputtering to limit advancement of the negtive gasions toward the component to prevent the negative gas ions frompuncturing the thin dielectric films.

5. A coating method for providing a thin dielectric layer of apredetermined suptterable material on a thin film component, thecomponent including thin dielectric and thin metal films depositedalternately on a non-conductive substrate, the component being mountedon a support in a rarefied, reactive gas atmosphere which both supports,between an anode and a cathode, a sputtering gas discharge and whichcomprises a mixture of reactive and nonreactive gases, both of whichinclude negative gas ions, which method comprises:

positioning an electrode in the discharge and impressing a potentialthereon substantially the same as the potential on the support toestablish a substantially field-free region adjacent to the componentand extendingaway from the component a distance greater than themean-free path of the negative gas ions, said field-free region having apotential gradient which is essentially zero; and

reactively sputtering neutral atoms of the predetermined materialthrough said field-free region onto the component, said atoms and thereactive gas combining on the surface of the component to form thedielectric layer, said field-free region being effective during saidsputtering to limit advancement of the negative gas ions toward thecomponent to prevent both types of negative gas ions from puncturing thethin dielectric films and to prevent the negative reactive gas ions fromoxidizing the thin metal films.

6. A coating method for providing a layer of an oxide of tantalum atleast 300 angstroms thick on a thin film component, the componentincluding thin dielectric and thin metal films deposited alternately ona substrate, the component being mounted on a support in a rarefied,reactive gas atmosphere which both supports, between an anode and acathode, a sputtering gas discharge and which includes a noble gas andoxygen gas, said oxygen gas being at a partial pressure of from 4 to 18microns, said reactive gas atmosphere including negative oxygen ions,which comprises:

positioning an electrode in the discharge and impressing a potentialthereon substantially the same as the potential on the support toestablish an essentially field-free region adjacent to the component,the field-free region extending away from the component a distance ofone-half inch, said distance being greater than the mean-free path ofthe negative 11 oxygen ions at a total pressure of from 30 to 100microns;

reactively sputtering tantalum particles from the cathode held at apotential of negative 2550 volts, said tantalum particles being advancedthrough said essentially field-free region onto the component, saidfield-free region being effective during said sputtering to preventacceleration of the negative oxygen ions toward the component after thenegative oxygen ions undergo collisions with ions of the oxygen andargon gases within said region, to prevent the negative oxygen ions fromboth puncturing the thin dielectric films and from oxidizing the thinmetal films, said sputtering being sustained for a least 80 minutes.

7. A method of sputtering thin films from a cathode to an anode,comprising the steps of:

bombarding said cathode with ions to free atoms therefrom said ionsbeing produced by making the potential of said cathode negative withrespect to said anode;

forming a field-free region about said anode by making the potential ofa grid, which grid is positioned between said anode and said cathode, atleast as anodic as that of said anode;

depositing said cathode atoms on said anode, said cathode atomstraveling through said field-free region, so that negative impurity ioncontamination of said deposit is reduced.

8. A method of sputtering thin films from a cathode to an anode, whereinnegative ions do not impinge upon said anode, comprising the steps of:

bombarding said cathode with ions to free atoms therefrom, said ionsbeing produced by applying a voltage to said cathode so that itspotential is negative with respect to that of said anode;

forming a field-free region about said anode by making the potential ofa grid positioned between said anode and said cathode, substantiallyparallel thereto, and

outside the cathode dark space distance, at least as anodic as that ofsaid anode;

depositing said cathode atoms on said anode, said cathode atomstraversing said field-free region to impinge upon said anode.

9. A method of sputtering thin filmsfrom a cathode,

comprising the steps of:

bombarding said cathode with ions to free atoms therefrom, said ionsbeing produced by making the potential of said cathode negative withrespect to said anode;

forming a field-free region about said anode by making the potential ofa grid, which grid is positioned between said anode and said cathode, atleast as anodic as that of said anode; and

depositing said cathode atoms on said anode, said cathode atomstraveling through said field-free 4/1962 France.

OTHER REFERENCES Bertelsen et al., IBM Tech. Disclosure Bulletin, vol.6, No. 11, April 1964, p. 45.

ROBERT K. MIHALEK, Primary Examiner U.S. Cl. X.R. 204-298

